A phase 2/3 clinical trial testing the safety, tolerability, efficacy, pharmacokinetics, and pharmacodynamics of GBT601, a drug candidate for sickle cell disease (SCD) by GBT has just started.

The randomized, multicenter study is made of 2 phases. The first phase will identify the optimal dose of treatment that will be used in the pivotal second phase.

“The initiation of our Phase 2/3 trial is an important milestone in our efforts to bring GBT601 to patients,” Kim Smith-Whitley, MD, executive vice president and head of research and development of GBT, said in a press release. “We anticipate that initial data from this trial as well as data from the continuation of our GBT601 Phase 1 study will be available before the end of the year.”

The trial aims to recruit a total of 480 participants with SCD, aged 6 months to 65 years in the US, Europe, Middle East, Africa, and South America.

In the first phase of the trial 60 patients, aged 18 to 65 years will receive a daily maintenance dose of 100 mg, 150 mg, or up to 200 mg of GBT601. The primary outcome measure of this phase will be the number of participants with a change in hemoglobin levels from baseline to week 12. Secondary outcomes measures will include pharmacokinetic and pharmacodynamic measures as well as the relationship between the treatment and measures of anemia and hemolysis.

Read more about voxelotor

Once the optimum dose of GBT601 is established, the trial will test its safety and efficacy in children and adults with the disease for 48 weeks compared to a placebo. An additional study arm will evaluate the safety and pharmacokinetics of single and multiple doses of GBT601 in children with the disease.

GBT601 is a next-generation sickle hemoglobin polymerization inhibitor. It has the same mechanism of action as voxelotor, also developed by GBT and approved by the US Food and Drug Administration for the treatment of SCD. However, GBT601 has the potential to achieve higher hemoglobin levels at a lower dose, according to the company. 


GBT initiates phase 2/3 clinical trial of GBT601 in patients with sickle cell disease. News release. GBT; June 29, 2022.

A phase 2/3 study in adult and pediatric participants with sickle cell disease (SCD). US National Library of Medicine. Updated June 24, 2022. Accessed June 30, 2022.